Generally, an engine control unit of a car is installed in a location away from the engine such as a car room where persons get in or a freight location. An automatic speed regulator control unit of a car is similarly installed in a location away from the automatic speed regulator. A control unit installed in this way is operated at the intra-car-room temperature and atmospheric temperature.
In recent years, from the viewpoint of reduction of the harness to be used inside a car and space reservation in a car room, such a control unit is apt to be installed in a control object itself or in the neighborhood of the control object. In such an installation location, for example, an engine control unit or a throttle control unit which is a control unit directly arranged in the engine, when the engine is in operation, is cooled by the flow of air or circulation of cooling water. Further, an automatic speed regulator control unit directly arranged in an automatic speed regulator, when the engine is in operation, is cooled by circulating gear oil for lubricating the speed change gear. Furthermore, a control unit installed integrally with a gear case for switching two-wheel drive and four-wheel drive of a car, in the same way as with the automatic speed regulator control unit, is cooled by circulating gear oil.
However, when the engine is stopped once, the circulation of cooling water is stopped and the cooling function is lost, so that the aforementioned control units rise in temperature once higher than that during operation of the engine and then is naturally cooled. A recent control unit is installed in the neighborhood of a control object as mentioned above and used in a severe state, thus a semiconductor integrated circuit and a semiconductor device used in a control unit are used at the semiconductor operation guarantee limited temperature (125° C. as a standard) at the highest.
In other fields of a computer system and a semiconductor manufacturing device, control units for protecting an object of a computer system or a semiconductor manufacturing device from abnormal heating when a temperature error occurs are indicated below.
[Patent Document 1]
Japanese Application Patent Laid-open Publication No. Hei 10-307635.
[Patent Document 2]
Japanese Application Patent Laid-open Publication No. 2001-267381.